8_ANOVA1 - ANOVA 1 Introduction to Analysis of Variance...

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Unformatted text preview: ANOVA 1 Introduction to Analysis of Variance (ANOVA) What is ANOVA? • ANOVA is short for ANalysis Of VAriance • Used with 3 or more groups. • E.g., caffeine study with 3 groups: – No caffeine – Mild dose – Jolt group • Level is value, kind or amount of IV • Treatment Group is people who get specific treatment or level of IV Example Designs for ANOVA Between Subjects Design IV: 3 matches/wk G1 3 matches/wk +visualization G2 3 matches/wk + visualization + ritual G3 DV: points won 1 st match Points won 1 st match Points won 1 st match Repeated Measures (within subjects design) Grp1 Saline G1 Drug 1 G1 Drug 2 DV: Video Game Performance VGP Repeated Measures – Each Person Gets All Treatments • Advantages of repeated measures: 1. Control for individual differences. 2. Reduced number of participants. • Disadvantages: 1. Cannot always be done, e.g., sex as IV, lottery winnings as IV. 2. Reactions to treatments – carryover or contrast effects (racquetball example, surveys). Choosing a Design: 1. The number of Groups • Use 2 groups when the study contrasts something as a whole (e.g., type of psychotherapy, workbook, flight instruction) • Use 3 or more groups when – The IV has lots of levels, e.g., race, geog location, therapies for phobias – Treatments can be broken into meaningful pieces (training for racquetball, training for RM includes labs, workbooks, computers, etc.) – Continuous variables are reduced to levels for economy (dating service similarity to hi, med, low). Choosing a design 2: Between vs. Within Subjects • In between subjects designs, different people go to different groups. In within subjects designs, people go to multiple treatments. • Control – nuisance variable can be controlled using within S design (academic performance, physical differences). • Practicality – are people scarce? Are there carryover or reactivity effects? • Develop 2 designs as exercise. Review • What is the difference between within subjects and between subjects designs? • What are some influences over choice of the number of levels of a factor to include in a study? • What are some influences over the choice of whether to use a repeated measures design? Rationale for ANOVA (1) • Logic of t-test. – How do we know if a given mean difference is large? – The difference in means is compared to the standard error of the difference in means. – The size of the standard error depends on two things: the SD of the population and N, the sample size. Rationale for ANOVA (2) • Now we have at least 3 means to test, e.g., H : μ 1 = μ 2 = μ 3 . • Could take them 2 at a time, but really want to test all 3 (or more) at once....
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This note was uploaded on 05/21/2011 for the course PSY 3213 taught by Professor Staff during the Fall '08 term at University of South Florida.

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8_ANOVA1 - ANOVA 1 Introduction to Analysis of Variance...

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